feat(connector): network-as-subcatalog architecture, STAC compliance fixes, DCAT mapping migration

[Vishmayraj]

Summary

This PR extends the STAC 1.0 connector introduced in #195 with a network-as-subcatalog architecture, resolves a persistent dummy-data/schema issue that was blocking test verification, and migrates the DCAT-AP 3.0 mapping reference into the main repo ahead of dcat_transformer.py implementation.

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What's in this PR

Network-as-subcatalog architecture

• harvester.py now exposes two separate harvest queries, one for deployments using the Network entity, one without, so non-network deployments aren't forced through unnecessary grouping logic.
• Added build_stac_catalog_with_networks and its supporting helpers, restructuring the STAC output so each network is served as its own subcatalog rather than a single flattened top-level catalog.
• cache.py gained a per-network caching path, so network-scoped catalogs are written and invalidated independently of the base catalog.
• scheduler.py updated to call the new network-aware build functions.
• Fixed _item_nav_links, which still had hardcoded orphan-collection paths from before the network architecture existed and was producing broken navigation links for items outside any network.

STAC compliance fixes

• Transformer output now includes license and conformance fields for full STAC 1.0 compliance.
• Removed hardcoded configuration values from the connector; these are now sourced from config.py.

Testing/dummy-data bug -> now resolved

• Fixed a parameter crash, an environment variable default, and a delete-user issue in the dummy-data generation path (generator.py), and brought the database init scripts in line with the latest upstream schema.
• Root cause was a stale branch, and a fix for the underlying issue had already landed upstream. This had been blocking verification of the network architecture above via the testing infrastructure.

DCAT-AP 3.0 mapping migration started

• Migrated the DCAT-AP 3.0 field mapping reference doc from the pre-GSoC standalone research repo into docs/, reconciled against the current harvesting layer and network architecture.
• dcat_transformer.py implementation is scoped as the next PR.

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Notes

• The network architecture is functionally complete; automated test coverage against it is still pending and tracked as a follow-up.
• DCAT-AP mapping is migrated but not yet implemented, dcat_transformer.py remains a stub, as noted in feat(connector): STAC 1.0 connector - harvesting, transformation, scheduling, caching, and API layer #195.

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